How can meso compounds be recognized?

1 Answer
anor277
May 4, 2016

By their symmetry.

Explanation:

A #"meso"# compound is a symmetric #RS# compound, with an internal plane of symmetry, such that upon reflection, the #R# group maps onto #S#. There are thus 2 chiral centres, with #RS# or #SR# configuration. To demonstrate the phenomenon, a favoured molecule is #2,3-"butanediol"#, which has 3 stereoisomers, one of which is the #"meso"#. (Why does it not 4 stereoisomers: #R,R#; #S,S#; #S,R#; and #R,S#?)

If you have trouble vizualizing the symmetry or asymmetry, use a model. And do not be ashamed to do so. You have to (i) recognize the symmetry, and (ii) represent that symmetry on the printed page. Neither of these are trivial processes.

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